1. Field of the Invention
The present invention relates to an optical coherence tomographic imaging apparatus that captures an image of a subject using Optical Coherence Tomography (OCT), and a method thereof.
2. Description of the Related Art
An optical coherence tomographic imaging apparatus for capturing an image of an eye, such as OCT, allows three-dimensional observation of an internal state of retinal layers. Such an optical coherence tomographic imaging apparatus has been recently attracting attention as being useful in more accurately diagnosing diseases.
A time domain (TD-) OCT is a type of OCT in which a broad spectrum light source is combined with a Michelson interferometer. The TD-OCT is configured such that by scanning a delay in a reference arm, the interference light generated by a backscattered light of a signal arm and the light from the reference arm is measured to obtain information on depth resolution. However, high-speed image acquisition is difficult in the above described TD-OCT. To address this, as a method for obtaining the image at higher speed, a spectral domain (SD-) OCT which uses the broad spectrum light source and obtains an interferogram employing a spectroscope is known. Further, U.S. Pat. No. 5,321,501 discusses a swept source (SS-) OCT in which a single channel light detection device measures spectral interference by employing a high-speed wavelength swept light source as the light source.
In general, an OCT tomographic image is obtained using light of a wavelength band of 800 nm to 900 nm as illustrated in FIG. 13A. Japanese Patent Application Laid-Open No. 2008-209166 discusses obtaining, before obtaining the OCT tomographic image, an infrared observation image of a fundus using light of the wavelength band of 700 nm to 800 nm. Further, after obtaining the OCT tomographic image, a visible still image of a fundus is obtained using light of the wavelength band of 400 nm to 700 nm.
Furthermore, peaks of an absorption coefficient of water, which is a main component of a biological object such as a subject's eye, exist at 980 nm and 1200 nm in the vicinity of the wavelength of 1000 nm. Japanese Patent Application Laid-Open No. 2007-327909 discusses obtaining the OCT tomographic image using light of the wavelength band of 980 nm to 1200 nm to avoid being affected by the absorption coefficient peaks.
In general, it is known that since an optical path length difference is generated between light of different wavelengths, positional deviation of a focus position is generated. As a result, if the OCT tomographic image is obtained using light of the wavelength band of 980 nm to 1200 nm instead of 800 nm to 900 nm, the following occurs. When the OCT tomographic image is obtained after obtaining the infrared observation image, the positional deviation of focus position is increased compared with ever before. It thus becomes difficult to obtain a high-quality OCT tomographic image.